As solid-state imaging devices (image sensors) using photoelectric conversion elements detecting light and generating a charge, CMOS (complementary metal oxide semiconductor) image sensors have been put into practical use. CMOS image sensors have been widely applied as parts of digital cameras, video cameras, monitoring cameras, medical endoscopes, personal computers (PC), mobile phones and other portable terminals (mobile devices) and other various types of electronic apparatuses.
A CMOS image sensor, for each pixel, has an FD amplifier having a photodiode (photoelectric conversion element) and a floating diffusion layer (FD) layer. The mainstream of reading operations for the same is a column parallel output type selecting a certain row in a pixel array and simultaneously reading the pixels in a column direction.
In this regard, for improvement of characteristics, various methods for realizing solid-state imaging devices (CMOS image sensors) of a high quality of image having a high dynamic range (HDR) have been proposed.
Conventionally, in a solid-state imaging device, as a method for raising (extending) the dynamic range, for example, there are known a method of reading two types of signals having different storage times from the same pixel in the image sensor and combining these two types of signals to extend the dynamic range, a method of combining a signal of a pixel having a high sensitivity which has a small dynamic range and a signal of a low sensitivity which is extended in the dynamic range to thereby extend the dynamic range, and other methods.
For example, PTL1 discloses a technique for raising the dynamic range by dividing exposure into two or more steps of an image capture corresponding to a high luminance side by a short exposure time and an image capture corresponding to a low luminance side by a long exposure time. Further, PTL 1 discloses a technique for raising the dynamic range by making the capacity of the floating diffusion variable.
Further, PTL 2 discloses a technique for raising the dynamic range by connecting a floating diffusion of a small capacity C1 on a high sensitivity and low luminance side and a floating diffusion of a large capacity C2 on a low sensitivity and high luminance side to a photodiode PD and individually outputting an output OUT1 on the low luminance side and an output OUT2 on the high luminance side.
As the method of combining these signals, in terms of time, there is a system covering a plurality of frames, a system outputting two or more types of signals having different dynamic ranges in one frame, and the like.